A well established and senior investigator in the field of AT has proposed this work to improve the diagnosis and treatment of AT. The proposal aims to understand the relationship between specific mutations and clinical symptoms. Because as many as 1% of the general population may carry a defective ATM (A-T mutated) gene, and these individuals may compromise perhaps 5% of all cancer patients, it is hoped that these studies will also offer better diagnosis for AT-carriers. The ATM gene is large, with 66 small exons, thereby presenting a challenging technical problem for mutation screening. At UCLA, Dr. Gatti has a unique repository of cells, mRNAs, and DNAs from greater than 200 A-T patients and their families. This resource allowed him to play a major role in the positional cloning that led to the isolation of the ATM gene in 1995. Since then greater than 200 mutations have been defined; more than half of these have come from his laboratory. Almost all of these mutations have been detected by screening mRNA/cDNA, using a protein truncation test and conformation sensitive gel electrophoresis (CSGE). Dr. Gatti will complete the task of defining cDNA defects and their corresponding genomic (gDNA) mutations on the remaining cDNAs and their screen DNA on 100 additional patients from whom cDNA is not available. Dr. Gatti will use restriction endonuclease finger printing, chemical cleavage, and semi-automated single strand conformational polymorphism screening methods. He will also participate in testing the efficiency of "smart chips" and other newly-introduced screening techniques in order to minimize the amount of actual sequencing necessary to define each mutation. Since most patients are compound heterozygotes, his resources should allow the characterization of 400 mutations. Dr. Gatti will also determine the affected haplotypes for each patient and, whenever possible, within each family. He will then compare the type and site of each mutation with the clinical symptoms of patients from multiple-affected families and ethnic groups with founder effect mutations. Families with variant phenotypes will be studied. Dr. Gatti anticipates that his research project will ultimately help to define the single common biological mechanism that underlies this complex syndrome. Based on this understanding, he then hopes to design a rational approach to an effective therapy of the affected children.